Colorectal cancer causes more than 700,000 annual deaths worldwide and it is estimated that approximately 145,000 new cases of CRC will be diagnosed in the United States in 2023.2 In randomized trials, the relative risk of death from CRC was approximately 15% lower among persons who were assigned to undergo screening with stool-based testing. Similarly, in a pooled analysis of three randomized trials, the incidence of CRC was up to 25% lower after 10 to 12 years of follow-up among persons who had been invited to undergo CRC screening than among those who had not been invited.10 Although screening strategy is crucial in order to achieve effective management of CRC, OC is an invasive and uncomfortable modality for patients which frequently associated with incomplete, contraindicated and risky scanning as well. It is well-established that VC is considerably safe procedure with low risk of surgical complications and perforation than optical colonoscopy.7,9 In a multicenter study consisted of 16 centers across 5 countries Pickhardt reported an overall perforation rate of 0.009% in 21,923 studies with VC.10 Additionally, in a meta-analysis Kumar et al. compared VC and OC techniques in 49 studies; researchers concluded that both procedure had statistically equivalent performance for detecting CRC.11 Similarly, Mohammad et al. documented VC sensitivity, specificity, and accuracy of 100%, 93.75%, 96.88% respectively for detection of mass in colon; 75%, 100%, 87.50% respectively for polyps and 100% for diverticulum in 50 patients with colorectal symptoms.12 Supportively, Kim et al. compared results of VC and OC screening in a large sample group which consisting of randomly enrolled 3120 VC and 3163 OC patients. Researchers documented 123 neoplasms during VC screening and 121 neoplasms during OC screening, moreover they noted 14 and 4 invasive cancers, respectively. Furthermore they reported 7 colonic perforations in the OC group. Thus, researchers highlighted that although both screening methods provides similar accuracy rates for advanced neoplasia, VC screening achieved significanlty lower polypectomy and complication rates. Researchers also recommended VC as a primary screening test method.13 In another study, He et al. documented the sensitivity and accuracy of VC versus OC in detection of polyps was 0.952, 0.906 and 0.783, 0.641 respectively in 345 patients who underwent curative surgery for CRC.14 In accordance with these data, we detected 3 polyps (15%); which were also confirmed by optical colonoscopy and no polyps were detected by OC in the remaining 17 patients.
The one of the most important advantages of VC technique is that high diagnostic accuracy for polyps larger than 1 cm in diameter.8 In a study with 1233 asymptomatic adults, Pickhardt et al. reported overall sensitivity of VC and optical colonoscopy for adenomatous polyps were 93.8% and 87.5% (> 10 mm ), 93.9% and 91.5% (> 8 mm), 88.7% and 92.3% (> 6 mm), respectively. The specificity of VC was 96.0% (> 10 mm), 92.2% (> 8 mm), and 79.6% (> 6 mm). Researchers concluded that VC accuracy was favorably to optical colonoscopy for screening method of CRC in asymptomatic adults.15 Similarly, in a multicenter prospective study Johnson et al. documented the sensitivity, specificity, positive and negative predictive values of 0.90, 0.86, 0.23, 0.99 per-patient, respectively for adenomas > 10 mm size in 2600 asymptomatic adults. Researchers also noted VC accuracy of 90% for large adenomas.16 On the contrary, Chini et al. highlighted that VC exhibits poor performance in detecting flat lesions or lesions lower than 5 mm diameter in their meta-analysis involving 18 articles. However researchers also stated that these lesions rarely represents malignant potential.17 Furthermore, Sha et al. reported that OC could not detect suspicious polyps lower than 2.2 mm, on the other hand this threshold was 0.6 mm for VC in their study conducted with 318 VC and 318 OC patients. Thus, researchers concluded that VC is higly sensitivity than OC for detection of CRC in symptomatic patients.18 Consistently polyps detected in present study were with a diameter of 6 mm in the sigmoidal region, 3 mm in the hepatic flexure region, and 4 mm in the retrosigmoidal region.
Limited number of published data evaluated management of narrowness and difficult sections of colon for the supine and prone positions during VC examination. Barra et al. demonstrated that evaluating the VC findings in combination of supine and prone positions provides more accurate assessment particularly in narrow segments of colon than other imaging techniques for the diagnosis of bowel endometriosis.19 Supportively, Yee et al. concluded that combination of supine and prone VC scanning significantly achieved higher sensitivity of polyp detection than supine or prone positions individually (p < 0.001). Researchers documented sensitivity for detection of polyps with all sizes (< 5 mm, 5.0–9.9 mm, > 10 mm) was 69.9% by combined scanning, 42.1% by supine scanning and 36.3% by prone scanning in 182 patients.20 In present study, for the both supine and prone examinations, the distal descending colon was determined to be the most challenging site. In addition, the mean descending colon diameter calculated in the prone position was found to be statistically larger than the mean descending colon diameter calculated in the supine position.
In conclusion, our findings clearly demonstrated that combination of prone and supine scanning provides clear field of vision on narrow parts of the colon which improves accurate estimation for polyp detection. Furthermore, VC appears to be more comfortable, safe, fast, and cost-efffective procedure for CRC screening with advantages of low radiation exposure, extracolonic findings and lack of sedation requirements. Additionally, it is obvious that VC is useful for incomplete, contraindicated, risky OC scanning or reluctant patients. In this respect, comparison of the present findings with further data from larger study groups may contribute to diagnosis and management of CRC.